Measurements.—Average and extreme measurements, in millimeters, of twenty mature specimens from the Yosemite section of the high Sierra Nevada are as follows: Ten males: total length, 263 (230–280); tail vertebræ, 66 (60–74); hind foot, 44 (41–45.5); ear from crown, 9 (7–11); greatest length of skull, 44.5 (42.2–46.3); zygomatic breadth, 28.0 (26.4–29.5); interorbital width, 10.5 (9.7–11.0). Ten females: total length, 260 (240–288); tail vertebræ, 66 (55–74); hind foot, 43 (40–46); ear from crown, 10 (8–13); greatest length of skull, 44.0 (41.3–46.5); zygomatic breadth, 28.2 (26.7–28.9); interorbital width, 10.4 (9.7–11.0).
Relatively old individuals show greatest size, especially of skull, which also has acquired more conspicuous ridges and sharper angles. Males average a trifle larger than females.
Weights.—Average and extreme weights, in grams, of twenty mature specimens from the Yosemite section of the high Sierra Nevada are as follows: Ten males, 222 (125.5–285.0); ten females, 240 (172–305). Average, in ounces, both sexes, about 8.
The example showing the least weight was fully adult, but was very lean. Like other ground squirrels this species varies greatly in weight according to the amount of fat present. Specimens taken in August and September are, as a rule, fattest.
Type locality.—Donner, Placer County, California (Merriam, 1888, pp. 317–320).
Distribution area.—Higher parts of the central Sierra Nevada (chiefly Hudsonian life-zone), from vicinity of Independence Lake, Nevada County, south to southeastern border of Yosemite National Park in vicinity of Mount Lyell (see fig. 18). Altitudinal range, from 11,800 feet (as on Mt. Conness) down on western flank of Sierras to as low as 8,100 feet (Porcupine Flat, Yosemite Park); on eastern flank to as low as 6,500 feet, at western border of Mono Lake (Mus. Vert. Zool.).
Specimens examined.—A total of 48 from the following localities in California: Nevada County: Independence Lake, 13. Placer County: "Johnson's Pass, High Sierras" [= Summit], 1. El Dorado County: Mt. Tallac, 1. Alpine County: Hope Valley, 4. Mono County: Mono Lake P. O., 1; Farrington's, Mono Lake, 3; Mono Pass, 1; Tioga Pass, 1; Walker Lake, 1. Tuolumne County: Tuolumne Meadows, 8; middle Lyell Canyon, 1; head Lyell Canyon, 5. Mariposa County: Mt. Hoffman, 10,700 ft., 1; Tioga Road, southeast Mt. Hoffman, 3; near Vogelsang Lake, 2; two miles east Porcupine Flat, 1; one mile east Lake Merced, 1.
This species of ground squirrel was named after Lyman Belding, an early resident of Stockton and a naturalist of considerable attainment. Belding found it in the summer of 1885 in the vicinity of Summit, Placer County, and sent a specimen to Dr. C. Hart Merriam, who later (1888) described the species, calling it Spermophilus beldingi.
The most notable thing about the Belding Ground Squirrel is the great altitude of most of the area it inhabits. It is very closely restricted to the alpine meadows of the high central Sierra Nevada. The warmer levels below seem to be just as inimical to its welfare as the cold upper zones certainly are to the other ground squirrels which inhabit the middle slopes or foothills. Reference to our diagram (fig. 23) will show some interesting facts in this regard. We would infer that the Belding Ground Squirrel is the hardiest of all our species as regards ability to endure long and cold winters, though here the habit of hibernation must come importantly into play as tiding it over the extremes.
This squirrel occurs in fair abundance on the preferred portions of its general range, namely, the grassy meadows in the neighborhood of timber line. Individuals rarely occur down as low as the belt of red firs and aspens (Canadian zone) on the west slope of the Sierras, though on the east slope a few do occur down through the Jeffrey pine belt. It is quite strictly an inhabitant of open levels; it is rarely or never seen in the woods or on steep or rocky slopes. Occasionally an individual ascends to the top of some glacier-borne boulder out in a meadow for a look around, but we have yet to observe any greater exploit in climbing.
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